1. Field
The present inventive concept relates to a conductive layered structure having a large specific surface area and a high conductivity, an electrode and a supercapacitor that include the conductive layered structure, and a method of preparing the conductive layered structure.
2. Description of the Related Art
Secondary batteries and electrochemical capacitors are typical examples of energy storage devices based on electrochemical principles. Secondary batteries have high energy density per unit weight or unit volume, but have short lifetime and low output density and take long time for charging. Electrochemical capacitors known as supercapacitors have about 1000 times or greater specific capacitance than common electrostatic capacitors, take less time for charging and have high output density, but have low energy density.
Supercapacitors or electrochemical capacitors that electrochemically store energy via electric double layers (EDLs) have high power output, long lifetime stability, and a rapid charge/discharge rate, and are environmentally friendly. Due to these advantages, much research has been conducted on them for applications in small, portable electronic devices.
Objectives in supercapacitor research are mostly to develop an electrode material having a high conductivity and a large specific surface area through simple processes at low costs. It is crucial to find out a material-process combination satisfying these requirements.
Methods of manufacturing a supercapacitor electrode may be classified into the following two categories. A first method is of manufacturing an electrode by increasing a specific surface area of a high conductive carbonaceous material. Use of carbonaceous materials is advantageous in terms of low price and easy processibility into various forms. For example, carbonaceous materials can be processed into powder, fiber, foam, fabric, or composite. Processing carbonaceous materials into various forms may involve a high-temperature process (800° C. or higher) for a high pore density. Also, in manufacturing an electrode using the resulting product, an insulating binder material is added thereto, the conductivity and the specific surface area of the material may be reduced due to the binder. A second method uses a stable metal material resistant to oxidation. The most common method is de-alloying, which involves preparing an alloy of metals, and selectively melting one of the metals to obtain a porous metal structure. However, this porous metal structure is highly vulnerable to damage during an etching process, and appropriate source metals resistant to oxidation in electrolyte solution are mostly expensive precious metals.
Biocompatible or implantable devices are harmless to the human body and implantable into a human organ. These artificial devices may be inserted into an impaired or abnormally operating human organ to relieve or recover the patient from the illness, and thus should be normally operable in physiological environments to satisfy both the requirements for biocompatibility (or non-cytotoxicity) and biofunctionality.
Existing implantable devices have been limited only to simple electrodes for reading electric signals or catheter. An implantable energy storage device has not been available yet.